Two Mautic - One Database of Contacts

Both Mautic versions are: 2.16

We are looking to merge the Database of contacts/emails we’ve sent from one Mautic Instance with the one of another Mautic Instance and be able to use the two instances simultaneously and have the data of a lead contacted from one instance to be reflected in the interface of the second instance.

Any idea how to achieve this? Support would be very much appreciated!